U.S. Pat. Nos. 3,872,226 and 3,863,004 disclose the preparation of macroaggregates denatured albumin having divalent tin bound thereto. A related disclosure can be found in U.S. Pat. No. 4,024,233. The macroaggregates referred to are suitable for tagging with technetium-99m, and when so tagged, can be used in perfusion lung scanning to obtain information about the pulmonary vasculature. The size of the macroaggregates must be of the order of about 5 to 100 microns so that when administered to a patient they will localize in his lungs.
U.S. Pat. No. 3,863,004 also discusses the labeling of denatured albumin microspheres with technetium sulfur colloid. It is stated, however, that the tagged microspheres tend to agglomerate, and that it is necessary to subject the agglomerated particles to an "appropriate technique" (ultrasonic treatment is suggested) to disperse them. U.S. Pat. No. 3,872,226 discloses the washing of the macroaggregates.
In addition to the above-described technetium-99m labeled macroaggregates of denatured albumin, the prior art also discloses the preparation of microaggregates of iodine-131 labeled denatured albumin (see Kutas et al., International Journal of Applied Radiation and Isotopes, 26:31 (1975)) and of microaggregates of technetium-99m labeled denatured albumin (see Yamada et al., Journal of Nuclear Medicine, 10(6):453 (1969) and Honda et al., Journal of Nuclear Medicine, 11(10):580 (1970)). These references utilize the term "microaggregates" to refer to an aggregate having a size in the range of about 1-3 microns. Such microaggregates localize in, and can be used to visualize, the reticuloendothelial system.
The microaggregate products disclosed by Kutas et al., supra., Yamada et al., supra., and Honda et al., supra., are not well suited for commercial use. The references teach the labeling of albumin followed by the subsequent ultrasonication of the labeled aggregates. This type of product is most impractical for large scale distribution. Such a product would require the user to accurately size the particles before administering the product to a patient.